Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 201419

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1019 AM EDT Wed Jul 20 2016

High pressure will build southeast across the area through this
evening before drifting offshore through Thursday. A cold front
will pass to the north Friday night with high pressure then in
control across the eastern states through Monday. A cool front
looks to enter the area Monday night and linger just south of the
area into the midweek.


As of 9am, upper 50s to low 60s dewpoints continue to spread
south across the area in a light north wind. A weak boundary looks
to linger over central Virginia through midday where dewpoints
will remain in the mid 60s.

Dry across the area today with the exception of an isolated
shower or thunderstorm possible across central Virginia into
extreme southern Maryland this afternoon into this evening...but
even across these areas most of the time will be dry.

High pressure will remain overhead for tonight...bringing dry and
comfortable conditions. Min temps mid 60s inland (around 60s west
of the Blue Ridge) and 70s near shore (water temps in the low


High pressure will weaken and move offshore Thursday into Thursday
night. A return flow will allow for slightly more humid
conditions...and max temps will be a few degrees hotter compared
to Wednesday with most areas topping off in the upper 80s to lower
90s. Min temps Thursday night will range from the 60s in the
Potomac Highlands and portions of the Shenandoah Valley to the
lower and middle 70s near Washington and Baltimore.

High pressure over the Atlantic will dominate the weather pattern
for Friday and Friday night. A subtropical ridge will also begin
to edge closer to the area...with the center of the ridge
remaining over the central Conus. The higher heights along with a
southwest flow will cause unseasonably hot conditions for Friday.
Max temps will be in the middle to upper 90s across most
locations...but cooler in the mountains. Do think that there may
be enough of a westerly component to the low-level flow for
dewpoints to mix down into the lower to middle 60s during peak
heating. If this occurs...then heat indices around 100 degrees are
expected. However...higher dewpoints may cause heat indices around
105 degrees and this cannot be ruled out at this time. Very warm
and humid conditions will persist for Friday night.


Heat will be the primary concern for the extended forecast. Area
will be influenced by westerly flow aloft, an artifact of the
broad ridge stretching across the Conus. Temperatures at 850 mb
will solidly reach 20C, and may even reach 22C. As a result, highs
will be well into the 90s if not approaching 100F.

Inherently there will be plenty of available instability given
the forecast heat. However, skill in forecasting placement and
timing of shortwaves in the extended forecast quite low. That will
be the key in determining which days have a thunderstorm threat.
If the ingredients were to assemble properly, an organized event
will be a possibility. Will refrain from those details at this

A cold front forecast to arrive by the end of the period. The
upper level pattern changes little though, so its effect may be


VFR conditions prevail under high pressure that builds today and
shifts offshore Thursday. Patchy fog may briefly reduce vsbys
during the early morning hours each day. A cold front passes north
of the area Friday night with chance thunder.

VFR anticipated this weekend under high pressure with a boundary
stalled south of the area. Its too early to determine whether
there will be a thunder threat.


A weak cold front will continue to shift south to southern MD
Chesapeake Bay waters through the rest of the morning. North winds
expected to peak at 15 knots or less. This boundary will stall
near or south of Smith Point today. High pressure will build over
the area through tonight and winds will be light. An isolated
shower or thunderstorm cannot be ruled out near Smith Point into
this evening...but even across this area most of the time will be

The high will move offshore Thursday and a return flow will
develop. A south to southwest flow will continue for Thursday
night through Friday night. Southerly winds may channel up the
middle portion of the Bay and Lower Tidal Potomac River...causing
winds to possibly reach SCA criteria during this time.

Summertime high pressure, with its heat and humidity, will be
affecting the waters this weekend. Such a pattern favors southerly
channeling late into the evening into the early morning hours.




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